1. Field of the Invention
The present invention relates to a guide rail supporting device, a guide rail device, a driving device and a measuring instrument.
2. Description of Related Art
There has been known a driving device having a guide rail as a guide mechanism, and there has also been known a measuring instrument with which a stylus is three-dimensionally displaced by this driving device to measure a form of a workpiece (refer to, for instance, Japanese Patent Publication No. HEI 3-45321).
In FIG. 8 is shown a coordinate measuring instrument 1 as an example of the measuring instrument.
The coordinate measuring instrument 1 comprises a stylus 2 applied onto a workpiece W for detecting a surface of the workpiece, a measuring table 3 having a table surface 31 for pulling thereon the workpiece W, a driving mechanism (driving device) 4 directly provided on the measuring table 3 for three-dimensionally moving the stylus 2, and a driving sensor (not shown) for detecting a driving quantity of the driving mechanism 4.
The driving mechanism 4 comprises a guide rail 41 provided straight in the Ym-axis direction along both side ends of the measuring table; two beam supporting bodies 42 each having a height in the Zm-axis direction, which is a substantially vertical direction from both side ends of the measuring table 3 toward the measuring table 3, and provided so that the guide rail 41 can slide in the Ym-axis direction; a beam 43 supported by an upper end of the beam supporting bodies 42 and having a length in the Xm-axis direction; a column 44 slidably provided in the Xm-axis direction in relation to the beam 43 and having a guide in the Zm-axis direction; and a spindle 45 slidably provided in the Zm-axis direction within the column 44 and holding the stylus 2 at a lower end thereof.
The guide rail 41 is integrated with the measuring table 3 along the side end of the measuring table 3 via a groove 41 A grooved at a slight distance from the side end of the measuring table 3.
The lower end of the beam supporting bodies 42 overpasses the guide rail 41, and the movement direction of the beam supporting bodies 42 is guided straight by the guide rail 41.
It is to be noted that the driving mechanism 4 has, for instance, a motor or the like as a driving section for moving the beam supporting body 42, the column 44 and the spindle 45, and this driving section is controlled for driving by a drive control section (not shown).
The driving sensor comprises, though not shown specifically, a Ym-axis sensor for detecting a movement of the beam supporting body 42 in the Ym-axis direction, an Xm-axis sensor for detecting a movement of the column 44 in the Xm-axis direction, and a Zm-axis sensor for detecting a movement of the spindle 45 in the Zm-axis direction.
For instance, the Ym-axis sensor comprises a scale member having a length measuring direction in the Ym-axis direction and provided on the guide rail 41, a detecting section provided at the lower end of the beam supporting body 42 for detecting displacement in relation to the scale member.
With the configuration as described above, the stylus 2 is three-dimensionally moved by the driving mechanism 4, and then a drive quantity of the driving mechanism 4 is detected by a driving sensor at the time when the stylus 2 is applied onto the workpiece W. Thus a form of the workpiece W is measured.
At this time, the beam supporting body 42 is guided straight by the guide rail 41, so that a drive thereof is smooth and a speed thereof is also fast. Further, straightness of a scale member is maintained by the guide rail 41, so that a drive quantity of the beam supporting body 42 is detected accurately by the Ym-axis sensor. Then a detected value by the Ym-axis sensor is analyzed in addition to a drive quantity of the column 44 and the spindle 45 to correctly measure a form of the workpiece W.
There occurs a problem, however, that, because the guide rail 41 is integrated with the measuring table 3, the guide rail 41 and the measuring table 3 cannot maintain each form independently to each other, so that, when one is deformed, the other is correspondingly deformed.
For instance, when a workpiece W is put on the table surface 31, as shown in FIG. 9A, there is a disadvantageous possibility that the central part of the measuring table 3 is dented and become curved owing to weight of the workpiece W. The result is that the guide rail 41 also becomes curved.
Or, when one edge of the measuring table 3 and another edge thereof have a different temperature to each other, this temperature difference generates a difference in displacement (thermal expansion quantity) between one edge and another edge. Then, as shown in FIG. 9B, the difference in displacement of the two ends generates deformation in the measuring table 3, so that the guide rail 41 provided on one edge and another edge of the measuring table 3 is deformed.
When the guide rail 41 is deformed as described above, there occurs a problem that the beam supporting body 42 is not guided straight and is deviated from a proper track.
When the guide rail 41 becomes curved, a distance between the two beam supporting bodies 42 is changed, thereby the beam 43 is also deformed and a position of the column 44 is changed, too. As a result, an error is generated in the position of the stylus 2, so that there occurs a problem that measuring accuracy is deteriorated. Further, when the guide rail 41 becomes curved, harmful loading imposed on the driving mechanism 4 is increased, which degrades a driving performance of the driving mechanism 4. For instance, when the guide rail 41 becomes curved, sliding resistance between the guide rail 41 and the beam supporting body 42 changes, so that loading imposed on a driving section also changes. As a result, control characteristics change, which increases unnecessary harmful vibration. Further, when harmful loading imposed on the driving mechanism 4 is increased, a portion thereof subject to sliding is intensively abraded. Then an economic loss such as deterioration in a life cycle thereof as a product, an increase in cost of maintenance or the like is caused.
Further, when the guide rail 41 becomes curved, the scale member is also curved, so that there occurs a problem that measuring accuracy of the driving sensor is deteriorated. Degraded measuring accuracy of a stylus coordinate not only leads to an error in measuring, but also generates an error in positioning of the stylus 2.
With the problems described above occurred when the guide rail 41 becomes curved, it has been difficult to improve the driving performance (including track accuracy, driving speed and positioning accuracy) and also to improve detecting accuracy of the driving sensor.